In many devices in which a gas stream is generated, the mass or volume flow of this gas stream must be monitored for safety reasons. Examples of such a device are, among other things, gas-measuring devices, i.e., devices for measuring a concentration of a gas in a gas stream, in which a measuring chamber is supplied with a gas stream via a feed line, but also blower filter devices, which supply a user with filtered air.
For example, it happens regularly, in gas measuring technology, that the measuring device, i.e., a device for measuring a concentration of one or more gases in a gas mixture, cannot be brought to the site at which the concentration of the gas or gases in the gas mixture shall be determined. This site is also called the measuring site. The reasons herefor are numerous. For example, there may be no supply lines at the measuring site or no space is simply available at which a device for measuring a concentration of one or more gases could be permanently arranged. The measuring devices are also used in other cases to ensure that the concentration of a harmful or hazardous gas is below a limit or threshold value at a measuring site. The device, especially if the device is a portable or mobile device, cannot be brought directly to the measuring site in this case, either. The measuring site also often does not correspond to the position of the measuring device when leaks are sought.
A measuring chamber of the device, in which a sensor element is arranged for determining a concentration of at least one gas in the gas stream, is often supplied with the gas mixture in a manner other than by diffusion. The gas stream is fed, instead, actively via a flow generator, for example, a pump, via a feed line. To ensure that the device measures correctly, it is important that a sufficient quantity of fresh gas be transported from the measuring site into the measuring chamber and to the sensor element. In other words, the mass or volume flow of the gas stream generated by the flow generator, which flow flows into the measuring chamber through the feed line, must be monitored.
It is known in the state of the art that differential pressure-based or heat conduction-based sensors can be arranged for this in the feed line for determining the mass or volume flow. Not only is it expensive to manufacture these sensors, as a result of which they make the devices more expensive, but they also need additional energy during the operation. Additional heating elements must be arranged in the gas stream especially if heat conduction-based sensors are used in order to heat the gas stream. However, the energy consumption of these heating elements is not negligible. This is especially relevant when the device for determining a concentration of a gas is a portable or mobile device, in which the entire quantity of energy consumed is provided by means of batteries. Thus, the energy demand of the heating elements shorten either the operating time of the device, or batteries having a higher capacity, which increase the weight of the portable device, must be used. It is meaningful to reduce the power consumption not only from the viewpoint of increasing power costs, but for ecological reasons as well even in stationary devices that have a permanent energy supply.